Burglar alarm system

ABSTRACT

A protective alarm system for a vehicle or the like wherein a protective switch initiates operation of a circuit combining two timing effects : effecting time delaying of an alarm device, and determining the duration of the alarm. Once initiated by the protective switch, the alarm is actuated after a predetermined delay and for a predetermined duration despite any action on the switch such as a periodical opening and closing. Circuitry operated by a key switch defeats instantaneously actuation of the alarm system when a further manually operated knob is on, which results in a necessary order of operation, involving the possession of the key, to inhibit definitely the alarm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

A protective alarm system for motor vehicle or the like is provided with a compact solid-state circuitry. Once actuated by a protective switch, the circuitry initiates the alarm after a predetermined delay and for a predetermined duration unless a definite succession of manual operations, involving the possession of a key, is carried out.

2. Description of the Prior Art

Burglar alarm systems are known comprising a first timing circuit which is operated by one or more protective switches and which in turn controls a second timing circuit, thereby to control the operation of an alarm circuit. Activation of the system is initiated by unauthorized tampering with a door, window or the like. A third key-operated timing circuit provides for activation of the protective circuit only after a predetermined time. See U.S. Pat. No. 3,659,266 to MEYERLE.

In such systems of the prior art, the alarm keeps operating for a predetermined time despite reclosing of the entrance. But if the reclosing occurs before the alarm is initiated (that is before the end of the first timing-circuit delay), the system resets itself in the initial conditions. Then, if a burglar or his accomplice opens and shuts the door with a period less than the time delay of the first timing circuit, the alarm is not triggered, and the burglar is able to operate at ease, as long as necessary for his evil-minded action.

Another drawback of a prior art burglar alarm system of that type is the considerable number of the components therein which are required by the structural or physical separation of the first and second timing circuits. SUMMARY OF THE INVENTION

An object of the present invention is a new circuit combining said first and second timing circuits, which results in an important reduction of the number of the components, thus reducing the cost and increasing the viability of the system.

The applicant has visualised for this purpose and has utilised a combined circuit which satisfies the two time-delay functions. It comprises a first capacitor shunted by a first resistance to introduce a time constant into the discharge, a second capacitor having one time constant with respect to the charge introduced by a second resistance and a second time constant with respect to the discharge introduced by the first resistance, and a diode shunting the second resistance. The first resistance and the second resistance are preferably adjustable.

Another object of the invention is to provide a key-operated timing circuit which is directly dependent on a key, for example the ignition key of the vehicle engine, and which is capable of being set by means of a two-position knob, so that a warning is triggered at the completion of the warning delay period when the delay-action triggering unit is set, whatever may be the position of the knob.

This circuit causes activation or deactivation of the protective system. It is included in the supply circuit of this protective system. It comprises an electronic gate which is formed of two transistors, a capacitor, the charge or discharge state of which controls the opening or closing of the electronic gate and means for charging or discharging the capacitor under the control of the two-position knob and a switch. The switch is preferably controlled by the ignition key of the vehicle.

For the purpose of charging the capacitor, it is necessary for the two-position knob to be closed for a period of time corresponding to the duration of the charging, and for the switch to be open (ignition key withdrawn); the delay-action control member is then set.

Once it is charged, the capacitor holds its charge for a considerable time, even if the switch is opened. Consequently, if a burglar gets into the vehicle and if he does not have the key for making contact before the warning-delay period expires, the alarm will be triggered on and will only be shut off at the end of the delay-action period, even if the burglar operates the two-position knob, which it will therefore not be necessary to conceal. The warning will not be stopped if the burglar cancels the means which has triggered the warning by reclosing the door for example.

In order to discharge the capacitor and thus to make the delay-action trigger device inoperative, it is necessary for the switch and the two-position knob to be both instantaneously closed.

The advantage of the two-position knob or button is that it permits the owner of the vehicle to cancel out, when necessary, the triggering of the warning signal without having to leave the ignition key in position.

BRIEF DESCRIPTION OF THE DRAWING

The sole FIGURE is a schematic diagram illustrating an exemplary embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

On this diagram, a double timing function is performed by the combination of two capacitors C₅ and C₆, two adjustable resistors R₈ and R₉ and one diode D₂ shunting R₉. R₈ is connected in parallel with C₅. A common terminal of C₅, R₈, D₂ and R₉ is connected to the plus terminal of a power supply, for instance the battery of the vehicle, through a diode D₃ and through the lighting bulb L of the vehicle. The conventional door contact switch 1 of this light is open when the door is closed. A common terminal of C₆, D₂ and R₉ is connected through a resistor R₄ to a pair of transistors TR₂ and TR₃ forming a Darlington circuit which controls a relay RL₃ actuating an alarm K. The same common terminal is also connected to other protective switches 2 and 3 (rear door, trunk etc. . .) through a diode D₁.

The plus terminals of condensers C₅ and C₆ are connected to the plus terminal of the battery. When contacts 1, 2 and 3 are open, C₅ and C₆ are normally discharged.

Disregarding the for the moment block 10 which controls the power supply of the Darlington circuit containing TR₂ and TR₃, it will be assumed that the power is supplied.

The aforementioned double timing function is obtained:

For the initiation of the alarm, by the charging time of the capacitor C₆ via the resistance R₉.

For the alarm period, by the discharge time through the resistance R₈ of the capacitor C₆ and of the capacitor C₅ mounted in parallel. D₂ passes or transmits current in this direction.

The parallel charging circuit of the two capacitors C₅ and C₆ comprises diode D₃ and the roof light contact 1. The closing of 1 produces the quasi-instantaneous charging of C₅, whereas that of C₆ is progressive and is a function of its capacitance and of the value of the resistance R₉ (for the charging of C₆, the diode D₂ has its poles in a direction which does not allow it to pass current.

When the door which controls the closure of the contact 1 is opened, C₅ is immediately charged and C₆ is progressively charged. Even if switch 1 is once again opened, the charging of C₆ then continues, with charge passing from C₅ by way of R₉. When C₆ is charged, it opens TR₂, which opens TR₃ and, thus causing RL₃ to be energised, for the entire period when switch 1 is closed. If now switch 1 is opened (by closing the door), C₅ and C₆, which are arranged in parallel with the dischage through the diode D₂, are discharged into R₈ during the warning period, which therefore depends on the sum of the capacitances of C₅ and C₆ and on the value of the resistance R₈.

If which one of the contacts 2 or 3 which is closed, C₆ and C₅ are immediately charged, the diodes D₁ and D₂ being transmissive or open in this direction. The diode D₃ prevents discharge into the roof light L. If I₂ is open and C₃ is charged (by a mechanism to be discussed later), the warning is initiated. If the contact 2 or 3 is opened, the duration of the warning is fixed, as previously, by the discharge of C₅ and C₆ into R₈.

This obviously assumes that the trigger device of block 10 is set and is feeding power to TR₂ and TR₃. The trigger device comprises two transistors TR₄ and TR₅ forming a Darlington circuit, a capacitor C₃ for fixing the voltage of the base of the transistor TR₄ by means of a resistance R₅ and which is capable of being charged by means of two series-resistances R₆ and R₇, by closing a two-position button or knob switch I₁. R₆ is shunted by a diode D₄, which is blocked to the charge of the capacitor C₃. I₁ is between R₆ and R₇. When I₁ is closed, the junction point 4 of R₆ and R₇ can be brought to a positive potential by closing a switch I₂.

The collectors of TR₄ and TR₅, which are in parallel, derive their negative feed from the capacitor C₆.

I₂ is a key-operated switch which is controlled by the ignition key T of the vehicle, and if this key is inserted and turned, I₂ is closed.

As a modification, the resistance R₇ can be omitted and the point 4 can be directly connected to the make-and-break terminal of the engine, which is positive when the ignition key is turned. The equivalent arrangement of FIG. 1, in which R₇ may be any arbitrary accessory, for example, a bulb, nevertheless enables the operation of the delay-action trigger device to be better understood, this operation being as follows:

It is first of all to be assumed that C₃ is discharged, this being obtained by closing I₁ and I₂ (D₄ is passing current with the discharge), and then by I₁ and I₂ being opened successively and in order.

If C₃ is discharged, the base of TR₄ is positive, and therefore TR₄ is non-passing and blocks TR₅. There is no supply to TR₂ and TR₃, RL₃ is at rest, even if the doors are opened, and even if the ignition key is removed. The vehicle is not protected. It is possible freely to open the doors, the trunk, and to change a wheel. In the circumstances as visualized, this could be called a position in which the thief may do as he pleases.

Before leaving the vehicle for taking a walk, the occupants will have to be careful to close trunk and all the doors, except one, and naturally to remove the ignition key, and then to close I₁ ; C₃ starts to be charged by way of R₆ and R₇, and it is then necessary quickly to close the last door. The vehicle is protected.

If a burglar gains access to the vehicle by breaking in, the warning signal will be triggered at the end of the delay period of C₆ ; if he again closes the door, this as previously, is without any effect, and in addition, if he operates I₁ (which is not concealed), this also has no effect.

Having returned to the vehicle, the owner will open the driver's door, ignition key in hand, and will take advantage of the delay action of the commencement of the warning for closing I₂, C₃ being quickly discharged through D₄. The owner then opens I₁. The vehicle is no longer protected.

If he returns to his vehicle simply for the purpose of picking up an object, he will leave I₂ closed for the necessary time. After this, he will close all the doors, except one, he will open I₂ and will arrange as previously for the delay action of the triggering of the warning for the closing of the last door. The vehicle is once again protected. 

I claim:
 1. An alarm system for use in a vehicle to detect unauthorized entry into the vehicle, comprising:A. a first switch means positioned to be operated when a door of the vehicle is opened, B. a key-operated switch means having at least first and second switch conditions, normally being in the first condition when the vehicle is empty, and adapted to be placed in the second condition by insertion and operation of a key, C. a two-position switch means which is manually operable between first and second switch positions, D. alarm means for giving an alarm when operated, E. disabling means operative only when the key-operated switch is in the second condition and responsive to placement of the two-position switch in the second switch position for disabling the alarm system, F. first delay means, operative only when the two-position switch is in the first switch position, and responsive to the act of placing the key-operated switch in the first condition, for beginning to measure a first delay interval, G. second delay means, fully operative only after the first delay interval has been measured to its conclusion, and responsive to operation of the first switch means, for beginning to measure a second delay interval, and H. third delay means, operative unless and until inhibited by placement of the key-operated switch means in the second condition, for defining a third delay interval during which the alarm means is operated.
 2. For use in a vehicle having a d.c. power supply, an alarm system for providing an alarm in response to unauthorized entry into the vehicle, said system comprising:A. switch means operated by said entry, B. alarm means, C. alarm energizing means connected to operate said alarm means, the energizing means being provided with an input terminal and, when activated by an activating signal to said input terminal, energizing said alarm means to produce said alarm, and D. activating means connected to said switch means for activating said alarm energizing means after a predetermined delay and during a predetermined duration in response to the operation of said switch means, wherein said activating means comprises1. an input capacitor connected across the terminals of said power supply through a circuit including said switch means,
 2. a first resistor shunting said input capacitor,
 3. an output capacitor coupled to said input capacitor through a second resistor shunted by a diode, and
 4. means for connecting said input terminal to the common terminal of said output capacitor and said second resistor.
 3. An alarm system according to claim 2, wherein at least one of the first and second resistors is adjustable.
 4. An alarm system according to claim 3, wherein said alarm energizing means further comprises an exit delay means controlled by a key switch and by a manual switch, said exit delay means including an RC network comprising a third capacitor connected to said power supply, a third resistor shunted by a diode in series with said capacitor, and a fourth resistor connected to ground, said manual knob being inserted between said third and fourth resistor, said key switch having a first terminal connected to the common terminal of said manual knob and of said fourth resistor, and having a second terminal connected to said power supply, said exit delay means further including means to inhibit said alarm energizing means when said third capacitor is discharged. 